THERMOSTAT?

Okay so theres no leaks, the water pumps works, im pretty sure its not the headgasket. And the heatercore has is bypassed. But the car is still over heating. It stopped for a couple days now its doing it again. When it gets hot I noticed the upper radiator hose is extremely pressurized as if the coolent isnt able pass back into the engine from the radiator. I also notice the radiatior seemed awfully cool after it over heated. So could it just be the thermostat not opening like its stuck closed maybe? Cuz the thermostat is right there where the hose attaches to the engine right? The way its seems to be overheating is the water/coolent will start to boil than pressureize the hole cooling system.

Yea the lower one is really hot. Actulluy it prolly needs to be replaced its swollen right where it ataches to the engine. But yea the lower one gets really hot. An the upper one gettz super pressurized. The coolent just seems to get hot than start boiling really hot than building up pressure than when I pop the overflow tank cap it shoot up like a geiser lol. Ima try replacing the thermostat. Tho.